The present application relates to the field of intervertebral cages and generally to the field of implants intended to be implanted between two adjacent verterbrae, to at least partly supplant an intervertebral disc to re-establish the height of the intervertebral space and the lordosis of the spinal segment, and more particularly to expansible vertebral implants of the intersomatic cage or corpectomy cage type.
To remedy certain pathologies, sometimes it is sought to obtain fusion of at least two adjacent vertebrae, for example when at least one of their adjacent intervertebral discs is lesioned.
From the prior art diverse arthrodesis techniques are known based on diverse types of implants, such as for example, intersomatic cages inserted into the place of a disc for re-establishing the height and the lordosis of the segment and for promoting bone growth (arthrodesis), to secure together two adjacent vertebrae.
Such devices are for example illustrated in French patent application FR1651637, which shows intersomatic cages giving the possibility of supplanting an intervertebral disc.
Further, to maximize the stability and graft volume contained in such implants and therefore the quality of the fusion, the latter have to cover a volume which is as close as possible to the volume occupied by the lesioned vertebral disc. The implants of the prior art therefore generally have a very large volume allowing their implantation relatively invasive for the patient.
One approach, used for reducing the size of the implants during their implantation and therefore their invasivity due to the necessary degradation during the route first, has been the use of expansible cages as for example described in European patent EP1699389 B1. Such cages, once they are implanted, are deployed by the surgeon, to cover a volume approaching the volume of an intervertebral disc, while having a profile allowing it to follow the lordosis of the vertebral column, thereby improving comfort for the patient and stability of the cage.
Nevertheless, this type of expansible cages includes a certain number of drawbacks. In particular, during their expansion, the surgeon has to exert an excessive pressure on the implant, notably because its expansion is simultaneously accomplished on two axes orthogonal with each other. Further, it is more difficult for the surgeon to observe a specific lordosis or to control the lordosis obtained. Finally, this type of implant does not rest or only very little on the cortical bone of the vertebra, but on a softer portion of the bone at the centre of the intervertebral space, which reduces its stability and has a risk of sinking.
In addition, for some devices disclosed in the prior art, the expansion of this type of cages is limited. Indeed, the final volume of the expanded cage is substantially identical to or a little greater than the initial volume.
Moreover, these implants often have a mechanism within the cage for allowing deployment. This mechanism occupies a significant portion of the graft space, and prevents the insertion of many grafts, which is detrimental to good fusion of the vertebrae.